Taking the Pith

Even as a dyed-in-the-wool botanist I have to admit that rushes (Juncus species) are pretty dull plants – just spiky bunches of cylindrical leaves growing in mud around pond margins (bottom picture) or dominating large areas of poorly drained upland pastures. But, as the old saying goes, ‘beauty is more than skin deep’ and to find the really attractive feature of this plant you have to delve below the leaf surface. Peeling back the outer layer of green photosynthetic tissue reveals a cylinder of spongy pith, as light as thistledown. Pith peeled from rushes and dipped in tallow was once used to form the wicks of rush-lights, a smoky-flamed form of interior lighting that was eventually replaced by gas mantles and then electric light. Take a look at these pith cells under the microscope, in a cross-section of the cylindrical leaf (see top picture) and their real beauty emerges. The individual cells, shaped like starfish, form three-dimensional interior scaffolding for the cylindrical leaf. Each ‘starfish-cell’ is joined to its neighbours by the tips of its arms, forming a three-dimensional lattice (see second picture from top). The top two photomicrographs were taken using fluorescence microscopy, where the section of the leaf was treated with a compound (in this case auramine) which fluoresces when illuminated with blue light, giving an very attractive green glow that shows the three dimensional structure of the plant tissue particularly well. Double-click the top image for a better view. To find out more about rush lights, visit http://pilgrim.ceredigion.gov.uk/index.cfm?articleid=1239